Light-emitting device and electronic device using the same

ABSTRACT

A lightweight flexible light-emitting device which is able to possess a curved display portion and display a full color image with high resolution and the manufacturing process thereof are disclosed. The light-emitting device comprises: a plastic substrate; an insulating layer with an adhesive interposed therebetween; a thin film transistor over the insulating layer; a protective insulating film over the thin film transistor; a color filter over the protective insulating film; an interlayer insulating film over the color filter; and a white-emissive light-emitting element formed over the interlayer insulating film and being electrically connected to the thin film transistor.

TECHNICAL FIELD

The present invention relates to a light-emitting device which has a circuit including a thin film transistor (hereinafter referred to as a TFT). Further, the present invention relates to an electronic device on which the light-emitting device is mounted.

BACKGROUND ART

In recent years, a technological development has been remarkably made in the field of displays. Especially, the needs of market has stimulated tremendous progress in the technology directed to increase in resolution and thinning of displays.

In a next phase, focus is placed on commercialization of a flexible display having a curved display portion. Indeed, a variety of proposals have been made on manufacturing the flexible display (for example, see Patent Document 1). The use of a flexible substrate enables reduction in weight of a light-emitting device compared with the use of a glass substrate.

However, such a flexible display is also required to have high image quality.

A variety of factors influence the image quality. For instance, improvement in resolution is effective for improvement of image quality.

[Patent Document 1] Japanese Patent Laid-Open No. 2003-204049.

DISCLOSURE OF INVENTION

However, a flexible substrate is readily deformed and twisted due to its flexibility. Therefore, an attempt to obtain full color display using a flexible substrate possesses a difficulty in precise and selective formation of light-emitting layers and color filters in an appropriate region of a display portion.

It is an object to supply a flexible light-emitting device which is able to have a curved display portion, has lightweight, and simultaneously can display a full color image with high resolution.

The foregoing problem can be solved by forming an element formation layer comprising a color filter and a thin film transistor over a plane substrate with a plate-like shape, such as a glass substrate, and then forming a white-emissive light-emitting element after transferring the element formation layer to a plastic substrate.

Namely, an embodiment of the invention is a light-emitting device comprising: a plastic substrate; an insulating layer formed over the plastic substrate with an adhesive sandwiched between the plastic substrate and the insulating layer; a thin film transistor formed over the insulating layer; a protective insulating film formed over the thin film transistor; a color filter formed over the protective insulating film; an interlayer insulating film formed over the color filter; and a white-emissive light-emitting element formed over the interlayer insulating film and electrically connected to the thin film transistor. Such a light-emitting device is able to display a full color image with high resolution in spite of its flexibility.

Another embodiment of the invention is a light-emitting device comprising: a plastic substrate; an insulating layer formed over the plastic substrate with an adhesive sandwiched between the plastic substrate and the insulating layer; a thin film transistor formed over the insulating layer; a first protective insulating film formed over the thin film transistor; a color filter formed over the first protective insulating film; a second protective insulating film formed over the color filter; an interlayer insulating film formed over the second protective insulating film; and a white-emissive light-emitting element which is formed over the interlayer insulating film and electrically connected to the thin film transistor. The light-emitting device is able to display a full color image with high resolution in spite of its flexibility. Additionally, the light-emitting device having this structure possesses improved reliability since the white-emissive light-emitting element is protected by the second protective insulating film from a gas released from the color filter.

Note that, in the above-mentioned structure, a light-emitting device is also included in an embodiment of the invention in which patterning of the color filter is performed to allow the color filter to be placed in a position corresponding to a first pixel electrode of the white-emissive light-emitting element, and the first protective insulating film and the second protective insulating film are in contact with each other in a vicinity of the color filter. The light-emitting device allows the white-emissive light-emitting element and the thin film transistor to be effectively protected from contamination resulting from degasification from the color filter and so on. Thus, a light-emitting device with more improved reliability can be obtained.

Note that it is preferred that the above-mentioned protective insulating film is a silicon nitride film because the silicon nitride film is able to more effectively block a contaminant and suppress degasification.

An embodiment of the invention is a light-emitting device comprising: a plastic substrate; a first insulating layer formed over the plastic substrate with an adhesive sandwiched between the plastic substrate and the first insulating layer; a color filter formed over the first insulating layer; a thin film transistor formed over a second insulating layer which is formed so as to cover the color filter; and a white-emissive light-emitting element formed over the thin film transistor and electrically connected to the thin film transistor. Even such a light-emitting device with this structure can be flexible and display a full color image with high resolution.

It is preferred that, in the light-emitting device with the above-mentioned structure, a semiconductor layer of the thin film transistor is formed of amorphous silicon, an organic semiconductor, an oxide semiconductor, or microcrystalline silicon since the thin film transistor is formed after forming the color filter.

The light-emitting devices of the embodiments of the invention can display a full color image with high resolution although they are flexible light-emitting devices.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are views each showing a light-emitting device of an embodiment of the invention;

FIG. 2 is a view showing a light-emitting device of an embodiment of the invention;

FIGS. 3A to 3D are diagrams showing a manufacturing process of a light-emitting device of an embodiment of the invention;

FIGS. 4A and 4B are views showing a light-emitting device of an embodiment of the invention;

FIGS. 5A to 5E are views each showing an electronic device according to an embodiment of the invention;

FIGS. 6A to 6C are views each explaining a structure of a light-emitting layer;

FIGS. 7A and 7B are views each explaining a structure of a light-emitting layer; and

FIG. 8 is a view explaining a structure of a light-emitting element.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the present invention can be carried out in many different modes. As is easily known to a person skilled in the art, the mode and the detail of the invention can be variously changed without departing from the spirit and the scope of the invention. Therefore, the present invention is not to be construed with limitation to what is described in the embodiment modes.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

A light-emitting device of an embodiment of the invention is characterized in that an element formation layer comprising a TFT, an electrode of a light-emitting element, and the like is supported by a plastic substrate through an adhesive and that a color filter is provided between the plastic substrate and the light-emitting element.

The light-emitting device having such a structure can be manufactured by the following method and the like. First, the element formation layer including the TFT, the color filter, and a first pixel electrode of the light-emitting element is formed over a substrate with low flexibility, such as a substrate formed of glass, ceramics, and the like, with a separation layer sandwiched between the element formation layer and the substrate. Next, the substrate and the element formation layer are separated from each other at the separation layer, and the separated element formation layer is bonded to the plastic substrate using the adhesive.

As to the light-emitting device manufactured in this way, the color filter is formed using the substrate having low flexibility. Therefore, even in the case of a pixel arrangement directed to a full color display in high resolution, misalignment of the color filter is negligible, which allows the formation of a flexible display capable of displaying a full color image with high resolution.

Note that a protective insulating film may be provided over the color filter in order to reduce adverse influence of degasification from the color filter upon the light-emitting element.

FIGS. 1A to 1C each illustrate a view showing the light-emitting device of the present embodiment.

In the light-emitting device shown in FIG. 1A, an adhesive 111 is provided over a plastic substrate 110. The adhesive 111 is provided so as to be in contact with an insulating layer 112, allowing an element formation layer 113 and the plastic substrate 110 to be bonded to each other. In the element formation layer 113, a pixel TFT 114, a TFT 115 in a driving circuit portion, a color filter 116, a first pixel electrode 117 of a light-emitting element 121 electrically connected to the pixel TFT 114, and a partition layer 118 are provided. FIG. 1A illustrates a part of these members. The light-emitting element 121 is formed of the first pixel electrode 117 exposed from the partition layer 118, an EL layer 119 which overlaps at least the first pixel electrode 117 and contains a light-emitting substance, and a second pixel electrode 120 which overlaps the EL layer 119.

Light emitted from the light-emitting element 121 is preferably red, green, blue, or white. The EL layer 119 and the second pixel electrode 120 of the light-emitting element 121 are formed after the element formation layer 113 is bonded to the plastic substrate 110. Note that since the EL layer 119 and the second pixel electrode 120 of the light-emitting element 121 are formed over all pixels in common, misalignment in the formation thereof does not provide a serious problem although they are formed using the plastic substrate 110.

In the light-emitting devices shown in FIGS. 1A to 1C, the color filter 116 is formed after the TFTs are formed. Note that it is preferred that the color filter 116 is formed over a first protective insulating film 122 which is provided over the TFTs since the first protective insulating film 122 is able to protect the TFTs from a contaminant released from the color filter 116.

FIG. 1B shows a structure in which a second protective insulating film 123 is provided over the color filter 116. This structure enables the production of a light-emitting device with higher reliability because adverse influence of degasification from the color filter 116 upon the light-emitting element 121 can be reduced.

FIG. 1C illustrates a structure in which the color filter 124 is patterned to be located on a position corresponding to the first pixel electrode 117 of the light-emitting element. In this structure, at least in a vicinity of the color filter 124, the first protective insulating film 122 and the second protective insulating film 123 which covers the color filter 124 are in contact with each other, which allows the color filter 124 to be completely surrounded by the protective insulating films. Therefore, diffusion of the contaminant from the color filter 124, such as a gas, can be more effectively prevented. Note that it is preferred that the first protective insulating film 122 and the second protective insulating film 123 are formed by using the same material. Moreover, these protective insulating films are preferably formed by using silicon nitride or silicon oxynitride which has a composition of nitrogen higher than that of oxygen.

Next, a manufacturing process of the light-emitting device of this embodiment is explained with reference to FIGS. 3A to 3D and FIGS. 1A to 1C.

First, the element formation layer 113 comprising the TFT, the color filter, the first pixel electrode, and the like is formed over the substrate 200 having an insulating surface with a separation layer 201 interposed between the element formation layer 113 and the substrate 200 (see, FIG. 3A).

As the substrate 200, a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate, a metal substrate over which an insulating layer is formed, and the like can be used. In the manufacturing process of the light-emitting device, the substrate 200 can be selected as appropriate in accordance with the conditions of the process.

Since a substrate with low flexibility, which is frequently used in the manufacture of usual displays, is used as the substrate 200, the pixel TFT and the color filter can be placed in an arrangement suitable for a high-resolution display.

The separation layer 201 is formed by a sputtering method, a plasma CVD method, a coating method, a printing method, or the like, so as to have either a single-layer structure or a stacked structure by using an element selected from tungsten (W), molybdenum (Mo), titanium (Ti), tantalum (Ta), niobium (Nb), nickel (Ni), cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and silicon (Si); an alloy containing these elements as a main component; or a compound containing these elements as a main component. A crystal structure of a layer containing silicon may be amorphous, microcrystal, or polycrystal. Note that the coating method includes a spin-coating method, a droplet discharge method, a dispensing method, a nozzle printing method, and a slot die coating method in its category here.

In the case that the separation layer 201 has a single-layer structure, it is preferred to form a tungsten layer, a molybdenum layer, a layer containing a mixture of tungsten and molybdenum, a layer containing an oxide or an oxynitride of tungsten, a layer containing an oxide or an oxynitride of molybdenum, or a layer containing an oxide or an oxynitride of a mixture of tungsten and molybdenum as the separation layer 201. Note that the mixture of tungsten and molybdenum corresponds to an alloy of tungsten and molybdenum, for example.

In the case where the separation layer 201 has a stacked structure, a tungsten layer, a molybdenum layer, or a layer containing a mixture of tungsten and molybdenum is formed as a first layer, and a layer containing: an oxide, a nitride, an oxynitride, or a nitride oxide of tungsten; an oxide, a nitride, an oxynitride, or a nitride oxide of molybdenum; or an oxide, a nitride, an oxynitride, or a nitride oxide of a mixture of tungsten and molybdenum is formed as a second layer.

In the case where the stacked layer of a layer containing tungsten and a layer containing an oxide of tungsten is formed as the separation layer 201, the layer containing tungsten may be formed first, which is followed by the formation of an insulating layer formed of an oxide (for example, a silicon oxide layer) over the layer containing tungsten so that a layer containing an oxide of tungsten is formed at the interface between the tungsten layer and the insulating layer. Further, a surface of the tungsten layer may be subjected to thermal oxidation treatment, oxygen plasma treatment, or treatment with a strong oxidizing solution such as water containing ozone to form the layer containing the oxide of tungsten. Further, plasma treatment or heat treatment may be performed in an atmosphere of oxygen, nitrogen, dinitrogen monoxide, or a mixed gas of these gases and another gas. The formation of a layer containing a nitride, an oxynitride, and a nitride oxide of tungsten can be similarly performed. Specifically, after forming the layer including tungsten, an insulating layer formed of a nitride, an oxynitride, or a nitride oxide (for example, a silicon nitride layer, a silicon oxynitride layer, or a silicon nitride oxide layer) is preferably formed over the layer including tungsten.

The insulating layer to be a base can be formed as a single layer or a stacked layer by using an inorganic insulating film such as silicon oxide, silicon nitride, silicon oxynitride, silicon nitride oxide, or the like.

As a material of the semiconductor layer included in the TFT, an amorphous semiconductor (hereinafter referred to as “AS”), a polycrystalline semiconductor, a microcrystalline semiconductor (semiamorphous or microcrystal, hereinafter referred to as “SAS”), a semiconductor which has an organic material as a main component, or the like can be used. The semiconductor layer can be formed by a sputtering method, an LPCVD method, a plasma CVD method, or the like.

Note that the microcrystalline semiconductor belongs to a metastable state which is an intermediate between an amorphous state and a single crystal state according to Gibbs free energy. That is, the microcrystalline semiconductor is a semiconductor having a third state which is stable in terms of free energy and has a short range order and lattice distortion. In the microcrystalline semiconductor, columnar-like or needle-like crystals grow in a normal direction with respect to a surface of a substrate. The Raman spectrum of microcrystalline silicon, which is a typical example of a microcrystalline semiconductor, is shifted to a small wavenumber region below 520 cm⁻¹ which corresponds to the wavenumber of the Raman spectrum peak of single-crystalline silicon. That is, the peak of the Raman spectrum of the microcrystalline silicon exists between 520 cm⁻¹ which represents single-crystalline silicon and 480 cm⁻¹ which represents amorphous silicon. The microcrystalline semiconductor includes at least 1 at. % of hydrogen or halogen to terminate a dangling bond. Moreover, a rare gas element such as helium, argon, krypton, or neon may be included to further promote lattice distortion, so that stability is enhanced and a favorable microcrystalline semiconductor film can be obtained.

The microcrystalline semiconductor film can be formed by a high-frequency plasma CVD method with a frequency of several tens to several hundreds of megahertz or a microwave plasma CVD method with a frequency of 1 GHz or more. Typically, the microcrystalline semiconductor film can be formed by using a gas obtained by diluting a silicon hydride or a silicon halide, such as SiH₄, Si₂H₆, SiH₂Cl₂, SiHCl₃, SiCl₄, SiF₄, or the like, with hydrogen. Additionally, the microcrystalline semiconductor film can be formed by using a gas containing a silicon hydride and hydrogen which is diluted by rare gas elements selected from helium, argon, krypton, and neon. In this case, the flow rate of hydrogen is set to be greater than or equal to 5 times and less than or equal to 200 times, preferably greater than or equal to 50 time and less than or equal to 150 times, much more preferably 100 times as much as that of silicon hydride.

A hydrogenated amorphous silicon can be typically exemplified as the amorphous semiconductor, while a polysilicon or the like can be typically exemplified as a crystalline semiconductor layer. Examples of polysilicon (polycrystalline silicon) include so-called high-temperature polysilicon that contains polysilicon as a main component and is formed at a process temperature greater than or equal to 800° C., so-called low-temperature polysilicon that contains polysilicon as a main component and is formed at a process temperature less than or equal to 600° C., polysilicon obtained by crystallizing amorphous silicon by using an element that promotes crystallization or the like, and the like. Note that as mentioned above, a microcrystalline semiconductor or a semiconductor containing a crystal phase in part of a semiconductor layer may be used.

As a material of the semiconductor, as well as an element of silicon (Si), germanium (Ge), or the like, a compound semiconductor such as GaAs, InP, SiC, ZnSe, GaN, SiGe, or the like can be used. Alternatively, an oxide semiconductor such as zinc oxide, tin oxide, magnesium zinc oxide, gallium oxide, indium oxide, an oxide semiconductor formed of a plurality of the above oxide semiconductors, and the like may be used. For example, an oxide semiconductor formed of zinc oxide, indium oxide, and gallium oxide may be used. In the case of using zinc oxide for the semiconductor layer, a gate insulating film is preferably formed using yttrium oxide, aluminum oxide, titanium oxide, a stack of any of the above substances, or the like. For a gate electrode layer, a source electrode layer, and a drain electrode layer, ITO, Au, Ti, or the like is preferably used. In addition, In, Ga, or the like can be added into zinc oxide.

In the case of using a crystalline semiconductor layer for the semiconductor layer, the crystalline semiconductor layer may be formed by any of various methods (such as a laser crystallization method, a thermal crystallization method, a thermal crystallization method using an element promoting crystallization such as nickel), and the like. Also, a microcrystalline semiconductor, which is an SAS, can be crystallized by irradiating laser light to increase its crystallinity. In a case where an element which promotes crystallization is not used, before the amorphous silicon film is irradiated with a laser beam, the amorphous silicon film is heated at 500° C. for one hour in a nitrogen atmosphere to reduce a hydrogen concentration in the amorphous silicon film to less than or equal to 1×10²⁰ atoms/cm³. This is because, if the amorphous silicon layer contains much hydrogen, the amorphous silicon layer may be destroyed by laser beam irradiation.

Any method can be used for introducing a metal element into the amorphous semiconductor layer as long as the method allows the metal element to exist on the surface of or inside the amorphous semiconductor layer. For example, a sputtering method, a CVD method, a plasma process method (including a plasma CVD method), an adsorption method, a method of applying a solution of a metal salt, or the like can be used. Among the above-mentioned processes, the method using a solution is convenient and has an advantage of easily adjusting the concentration of a metal element. It is preferable to form an oxide film on the amorphous semiconductor layer by UV light irradiation in an oxygen atmosphere, a thermal oxidation treatment, treatment with ozone water or hydrogen peroxide including a hydroxyl radical, or the like in order to improve wettability of the surface of the amorphous semiconductor layer and to spread the aqueous solution over the entire surface of the amorphous semiconductor layer.

The crystallization may be performed by adding an element which promotes crystallization (also referred to as a catalyst element or a metal element) to an amorphous semiconductor layer and performing a heat treatment (at 550° C. to 750° C. for 3 minutes to 24 hours) in a crystallization step in which the amorphous semiconductor layer is crystallized to form a crystalline semiconductor layer. As the element which promotes (accelerates) the crystallization, one or more of iron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), copper (Cu), and gold (Au) can be used.

In order to remove or reduce the element promoting crystallization from the crystalline semiconductor layer, a semiconductor layer containing an impurity element is formed in contact with the crystalline semiconductor layer and is made to function as a gettering sink. The impurity element may be an impurity element imparting n-type conductivity, an impurity element imparting p-type conductivity, a rare gas element, or the like. For example, one or a plurality of elements selected from phosphorus (P), nitrogen (N), arsenic (As), antimony (Sb), bismuth (Bi), boron (B), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) can be used. Specifically, the above-mentioned semiconductor layer containing the impurity element is formed in contact with the crystalline semiconductor layer containing the element which promotes crystallization, and heat treatment (at temperature ranging from 550 to 750° C. for 3 minutes to 24 hours) is performed. The element that promotes crystallization in the crystalline semiconductor layer is transported to the semiconductor layer containing the impurity element; thus, the element that promotes crystallization in the crystalline semiconductor layer is removed or reduced. After that, the semiconductor layer containing the impurity element functioning as the gettering sink is removed.

In addition, thermal treatment and laser light irradiation may be combined to crystallize the amorphous semiconductor layer. The thermal treatment and/or the laser light irradiation may be independently performed a plurality of times.

In addition, a crystalline semiconductor layer may be directly formed over the substrate by a plasma treatment method. Alternatively, the crystalline semiconductor layer may be selectively formed over a substrate by using a plasma treatment method.

As a semiconductor film mainly containing an organic material, a semiconductor film mainly containing carbon can be used. Specifically, pentacene, tetracene, thiophene oligomers, polyphenylenes, phthalocyanine compounds, polyacetylenes, polythiophenes, a cyanine dye, and the like are given as examples.

As to the gate insulating film and the gate electrode, a known structure may be applied, and a known method may be used for the formation thereof. For instance, the gate insulating film may be formed according to a known structure such as a single layer of silicon oxide, a stacked structure of silicon oxide and silicon nitride, and the like. The gate electrode may be formed of an element selected from Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Si, Ge, Zr, and Ba; or an alloy or a compound containing any of these elements as its main component by using the CVD method, the sputtering method, the droplet discharging method, or the like. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus, or AgPdCu alloy may be used. Either a single layer structure or a layered structure may be applied.

Note that although an example is shown in FIGS. 1A to 1C in which transistors with a top-gate structure are used, a transistor with a known structure such as a bottom-gate structure and the like may be used.

The first protective insulating film 122 is formed over the gate insulating film and the gate electrode. The first protective insulating film 122 may be formed of a silicon oxide layer, a silicon oxynitride film, a silicon nitride oxide film, or a silicon nitride film, or may be formed as a stacked film in which any of these films are combined. In any case, the first protective insulating film 122 is formed of an inorganic insulating material. The formation of the first protective insulating film 122 allows the reduction of pollution of the TFT caused by the color filter 116 formed later. The use of a silicon nitride film or a silicon nitride oxide film which has a composition of nitrogen higher than that of oxygen is preferred because the contaminant from the color filter 116 can be effectively blocked.

The color filter 116 is formed over the first protective insulating film 122. Although a color filter with a single color is shown in FIGS. 1A to 1C, a color filter which transmits red light, a color filter which transmits blue light, and a color filter which transmits green light are formed in an appropriate arrangement and shape. Any arrangement can be adopted for the arrangement of the color filter 116, including a stripe pattern, a diagonal mosaic arrangement, a triangle mosaic arrangement, an RGBW four pixel arrangement, and the like. The RGBW four pixel arrangement is a pixel arrangement having: a pixel mounted with a color filter transmitting red light; a pixel mounted with a color filter transmitting blue light; a pixel mounted with a color filter transmitting green light; and a pixel without color filter, and is effective in reducing power consumption and so on.

The color filter 116 can be formed by using a known material. In the case of using a photosensitive resin as the color filter 116, patterning of the color filter 116 may be performed by exposing the color filter 116 itself to light and then developed. It is preferred to perform patterning by dry etching when a minute pattern is formed.

After the formation of the color filter 116, an interlayer insulating film formed using an organic insulating material is formed over the color filter 116. As the organic insulating material, an acrylic, a polyimide, a polyamide, a polyimideamide, a benzocyclobutene-based resin, and the like can be used.

The second protective insulating film 123 may be provided between the color filter 116 and the interlayer insulating film in order to suppress the influence of degasification from the color filter 116 (see FIG. 1B). The second protective insulating film 123 can be formed with a similar material to that of the first protective insulating film 122. It is a preferred structure in which the second protective insulating film 123 is formed using a silicon nitride film or a silicon nitride oxide film having a composition of nitrogen higher than oxygen since degasification from the color filter 116 can be effectively suppressed. Note that a structure is preferred in which the first protective insulating film 122 and the second protective insulating film 123 are in contact with each other in a vicinity of the color filter 124 because influence of a contaminant and degasification can be more effectively suppressed (see, FIG. 1C). In this case, the use of the same material for the first protective insulating film 122 and the second protective insulating film 123 allows the improvement of adhesion therebetween, which contributes to further reduction of influence of the contaminant and degasification. The reduction of influence of the contaminant and degasification improves reliability of the light-emitting device.

After the formation of the interlayer insulating film, the first pixel electrode 117 is formed using a transparent conductive film. When the first pixel electrode 117 is an anode, indium oxide, an alloy of indium oxide and tin oxide (ITO), and the like can be used as a material of the transparent conductive film. Alternatively, an alloy of indium oxide and zinc oxide (IZO) may be used. In a similar manner, zinc oxide is also an appropriate material, and moreover, zinc oxide (GZO) to which gallium (Ga) is added to increase conductivity and transmissivity with respect to visible light may be used. When the first pixel electrode 117 is used as a cathode, an extremely thin film of a material with a low work function such as aluminum can be used. Alternatively, a stacked structure which has a thin layer of such a material and the above-mentioned transparent conductive film can be employed. Note that the first pixel electrode 117 can be formed by a sputtering method, a vacuum evaporation method, or the like.

Next, etching is performed on the interlayer insulating film, (the second protective insulating film 123), (the color filter 116), the first protective insulating film 122, and the gate insulating film to result in formation of a contact hole which reaches the semiconductor layer of the TFT. Then a conductive metal film is formed by a sputtering method or a vacuum evaporation method, which is followed by etching to result in an electrode of the TFT and a wiring. One of a source electrode and a drain electrode of the pixel TFT 114 is formed so as to overlap with the first pixel electrode 117 in order to achieve electrical connection therebetween.

After that, an insulating film is formed using an organic insulating material or an inorganic insulating material so that the insulating film covers the interlayer insulating film and the first pixel electrode 117. The insulating film is then processed to allow a surface of the first pixel electrode 117 to be exposed and an end portion of the first pixel electrode 117 to be covered by the insulating film, leading to the formation of the partition layer 118.

Through the above-mentioned process, the element formation layer 113 can be formed.

Next, the element formation layer 113 and a provisional supporting substrate 202 are bonded to each other using a first adhesive 203, which is followed by separation of the element formation layer 113 from the substrate 200 at the separation layer 201. By this process, the element formation layer 113 is placed over the provisional supporting substrate 202 (see, FIG. 3B).

As the provisional supporting substrate 202, a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate, a metal substrate on which an insulating surface is formed, and the like can be used. Further, a plastic substrate which can resist a temperature of the manufacturing process of this embodiment or a flexible substrate such as a film may be used.

As the first adhesive 203 used here, an adhesive, which is soluble in a solvent such as water or is capable of plasticizing upon irradiation of UV light, and the like, is used so that the provisional supporting substrate 202 can be chemically or physically separated from the element formation layer 113 when necessary.

Any of following methods can be applied in the transferring process from the substrate 200 to the provisional supporting substrate 202: forming the separation layer 201 between the substrate 200 and the element formation layer 113, forming a metal oxide film between the separation layer 201 and the element formation layer 113, embrittling the metal oxide film by crystallizing thereof, and separating the element formation layer 113; forming an amorphous silicon film containing hydrogen between the substrate 200 having high thermal resistivity and the element formation layer 113, removing the amorphous silicon film by irradiation with laser light or etching, and separating the element formation layer 113; forming the separation layer 201 between the substrate 200 and the element formation layer 113, forming a metal oxide film between the separation layer 201 and the element formation layer 113, embrittling the metal oxide film by crystallizing thereof, removing a part of the separation layer 201 by etching using a solution or a halogen fluoride gas such as NF₃, BrF₃, ClF₃, and the like, and performing the separation at the embrittled metal oxide film; and removing the substrate 200 over which the element formation layer 113 is formed mechanically or by etching using a solution or a halogen fluoride gas such as NF₃, BrF₃, ClF₃, and the like. Alternatively, a method may be used in which a film containing nitrogen, oxygen, or hydrogen (for example, an amorphous silicon film containing hydrogen, an alloy film containing hydrogen, or an alloy film containing oxygen) is used as the separation layer 201, and the separation layer 201 is irradiated with laser light to release the nitrogen, oxygen, or hydrogen contained in the separation layer 201, thereby promoting separation between the element formation layer 113 and the substrate 200.

When the above-described separation methods are combined, the transfer step can be conducted easily. For example, separation can be performed with physical force (by a machine and the like) after performing: laser light irradiation; etching to the separation layer 201 with a gas, a solution, or the like; and mechanical removal with a sharp knife, scalpel, or the like, so that the separation layer 201 and the element formation layer 113 can be easily peeled off from each other.

Alternatively, separation of the element formation layer 113 from the substrate 200 may be carried out after penetrating a liquid into an interface between the separation layer 201 and the element formation layer 113.

Next, the element formation layer 113 which is separated from the substrate 200 to expose the separation layer 201 or the insulating layer 112 is bonded to the plastic substrate 110 using a second adhesive 204 which is different from the first adhesive 203 (see, FIG. 3C).

As the second adhesive 204, various curable adhesives such as a reactive curable adhesive, a thermal curable adhesive, a photo curable adhesive such as an ultraviolet curable adhesive, an anaerobic adhesive, and the like can be used.

As the plastic substrate 110, a variety of substrates having flexibility and light-transmitting ability, a film of an organic resin, and the like can be used. The plastic substrate 110 may be a structure body comprising a fibrous body and an organic resin. It is preferred to use the structure body comprising the fibrous body and the organic resin as the plastic substrate 110 since resistivity to the breaking caused by bending is improved, and thus, reliability is increased.

The structure body comprising the fibrous body and the organic resin can be used as a film which can simultaneously function as the second adhesive 204 and the plastic substrate 110. In this case, as the organic resin of the structure body, a resin such as a reactive curable resin, a thermosetting resin, and a photo curable resin, and the like whose curing is promoted by an additional treatment are preferably used.

After the bonding of the plastic substrate 110 to the element formation layer 113, the provisional supporting substrate 202 is removed by dissolving or plasticizing the first adhesive 203. After the provisional supporting substrate 202 is removed, the first adhesive 203 is removed using a solvent such as water to allow a surface of the first pixel electrode 117 of the light-emitting element to be exposed (see, FIG. 3D).

Through the above-mentioned process, the element formation layer 113, which comprises the color filter 116, the TFTs 114 and 115, the first pixel electrode 117 of the light-emitting element, and the like, can be manufactured over the plastic substrate 110.

After the surface of the first pixel electrode 117 is exposed, the EL layer 119 is formed. A stacked structure of the EL layer 119 is not particularly limited. A layer containing a substance having high electron-transporting ability, a layer containing a substance having high hole-transporting ability, a layer containing a substance having high electron injection ability, a layer containing a substance having high hole injection ability, a layer containing a bipolar substance (a substance having high electron-transporting ability and high hole transporting ability), and the like are appropriately combined. For example, an appropriate combination of a hole injecting layer, a hole-transporting layer, a light-emitting layer, an electron-transporting layer, an electron injection layer, and the like can be performed. In this embodiment, a structure is explained in which the EL layer 119 comprises a hole injection layer, a hole-transporting layer, a light-emitting layer, and an electron-transporting layer. Specific materials to form each of the layers are given below.

The hole injection layer is a layer that is provided in contact with an anode and contains a material with high hole injection ability. Specifically, molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, or the like can be used. Alternatively, the hole injection layer can be formed using any one of the following materials: phthalocyanine compounds such as phthalocyanine (H₂PC) and copper phthalocyanine (CuPc); aromatic amine compounds such as 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (DPAB) and 4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl (DNTPD); polymer compounds such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS); and the like.

Alternatively, as the hole injection layer, a composite material comprising a substance with high hole-transporting ability and an acceptor substance may be used. It is to be noted that, by using the composite material comprising the substance with high hole-transporting ability and the acceptor substance, a material used to form an electrode may be selected regardless of its work function. In other words, besides a material with a high work function, a material with a low work function may also be used as the anode. As the acceptor substance, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F₄-TCNQ), chloranil, and the like can be given. In addition, a transition metal oxide is given. In addition, oxides of metals that belong to Group 4 to Group 8 of the periodic table can be given. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferable because of a high electron accepting property. Among these metal oxides, molybdenum oxide is especially preferable since it can be easily treated due to its stability in the air and low hygroscopic property.

As the substance having high hole-transporting ability used for the composite material, any of various organic compounds such as an aromatic amine compound, a carbazole derivative, an aromatic hydrocarbon, and a high-molecular compound (such as an oligomer, a dendrimer, or a polymer) can be used. The organic compound used for the composite material preferably has a hole mobility of 10⁻⁶ cm²/Vs or higher is preferably used. However, other materials than these materials may also be used as long as hole-transporting ability is higher than electron-transporting ability. The organic compound that can be used for the composite material is specifically shown below.

Examples of the aromatic amine compounds include N,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviated to DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviated to DPAB), 4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviated to DNTPD), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviated to DPA3B), and the like.

Examples of a carbazole derivative include 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphtyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1), 4,4′-di(N-carb azolyl)biphenyl (abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA), 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, and the like.

Examples of the aromatic hydrocarbons include 2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (DPPA), 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (t-BuDBA), 9,10-di(2-naphthyl)anthracene (DNA), 9,10-diphenylanthracene (DPAnth), 2-tert-butylanthracene (t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene (DMNA), 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl, 10,10′-diphenyl-9,9′-bianthryl, 10,10′-bis(2-phenylphenyl)-9,9′-bianthryl, 10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene, tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, and the like. As well as these compounds, pentacene, coronene, or the like can be used. Note that when a film of the above-mentioned aromatic hydrocarbons is formed by an evaporation method, the number of the carbon atoms participating in their condensed ring preferably ranges from 14 to 42 from the viewpoint of the evaporation behavior of the aromatic hydrocarbons and the quality of the formed film.

The aromatic hydrocarbon that can be used for the composite material may have a vinyl skeleton. As an aromatic hydrocarbon having a vinyl group, for example, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA), and the like are given.

The polymeric compounds are exemplified by poly(N-vinylcarbazole) (abbreviated to PVK), poly(4-vinyltriphenylamine) (abbreviated to PVTPA), poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide] (abbreviated to PTPDMA), poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviated to Poly-TPD), and the like.

The hole-transporting layer is a layer that contains a substance with high hole-transporting ability. Examples of the substance having high hole-transporting ability include aromatic amine compounds such as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbr.: NPB), N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (abbr.: TPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbr.: TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbr.: MTDATA), 4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl (abbr.: BSPB), and the like. The materials described here are mainly substances having hole mobility of 10⁻⁶ cm²/Vs or more. However, a material other than the above-described substances may be used as long as it has higher hole-transporting ability than electron-transporting ability. Note that the layer containing the substance with high hole-transporting ability is not limited to a single layer, and two or more layers containing the aforementioned substances may be stacked.

Further, a high molecular compound such as poly(N-vinylcarbazole) (abbr.: PVK) or poly(4-vinyltriphenylamine) (abbr.: PVTPA) can also be used for the hole-transporting layer.

The light-emitting layer is a layer containing a light-emitting substance. The light-emitting layer may be a so-called single layer light-emitting layer and a so-called host-guest type light-emitting layer in which a light-emitting substance is dispersed in a host material, as long as the emission from the light-emitting layer is located in the visible region. For example, followings are provided as the light-emitting layer: a light-emitting layer containing a light-emitting substance having a broad emission spectrum (see, FIG. 6A); a light-emitting layer containing a plurality of light-emitting substances having a different emission wavelength region (see, FIG. 6B); a light-emitting layer containing a plurality of layers which each include a light-emitting substance with a different emission wavelength region (see, FIG. 6C); and the like. These structures may be combined to each other. Note that in FIGS. 6A to 6C, a reference numeral 600 represents the first pixel electrode of the light-emitting element; a reference numeral 601 represents a second pixel electrode of the light-emitting element; a reference numeral 602 represents the EL layer; reference numerals 603, 603-1, and 603-2 each represent the light-emitting layer; and reference numerals 604, 604-1, and 604-2 each represent the light-emitting substance.

In the case of the structures shown in FIGS. 6B and 6C, a combination of the light-emitting substances (corresponding to the light-emitting substances 604-1 and 604-2, but being not limited to two kinds of substances) with different wavelength regions is generally exemplified by a combination of two kinds of light-emitting substances which emit light of complementary colors to each other (for example, blue light and yellow light) or by a combination of three kinds of substances with red, blue and green emission colors.

In the case of the combination of two kinds of light-emitting substances with complementary emission colors in the structure shown in FIG. 6C, it is preferred to employ a structure in which, as shown in FIG. 7A, a three-layer structure containing a first light-emitting layer 603-1, a second light-emitting layer 603-2, and a third light-emitting layer 603-3 in that order from a side of the first pixel electrode 600 is provided as the light-emitting layer 603; and a layer (the second light-emitting layer 603-2) containing a light-emitting substance 604-2 capable of emitting light with a long wavelength is interposed between layers (the first light-emitting layer 603-1 and the third light-emitting layer 603-3) each containing a light-emitting substance 604-1 capable of emitting light with a short wavelength. Note that, in the structure of FIG. 7A, carrier-transporting ability of each of the light-emitting layers is tuned by appropriately selecting host materials to allow recombination of electrons and holes to occur in the vicinity of an interface of the layer (the second light-emitting layer 603-2) containing the light-emitting substance 604-2 which is located on the side of the second pixel electrode 601 (i.e., an interface between the second light-emitting layer 603-2 and the third light-emitting layer 603-3). By using such structure, the lifetime of the light-emitting element can be improved, and the emission from the light-emitting substance capable of emitting light with the long wavelength and that from the light-emitting substance capable of emitting light with the short wavelength can be readily balanced.

Here, in the case where the first pixel electrode 600 and the second pixel electrode 601 are used as the anode and the cathode, respectively, “recombination of holes and electrons in the vicinity of an interface of the layer, containing the light-emitting substance capable of emitting light with the long wavelength, the interface of which is located on the side of the second pixel electrode, by tuning carrier transporting ability of each of the light-emitting layers through the appropriate selection of the host materials” can be achieved by designing the light-emitting element so that the layer (the third light-emitting layer 603-3), which is located on the side of second pixel electrode 601 and contains the light-emitting substance 604-1 capable of emitting light with short wavelength, has electron-transporting ability and the layer (the first light-emitting layer 603-1), which is located on the anode side and contains the light-emitting substance 604-1 capable of emitting light with the short wavelength, and the layer (the second light-emitting layer 603-2), which contains the light-emitting substance 604-2 capable of emitting light with the long wavelength, have hole-transporting ability. When the first pixel electrode 600 and the second pixel electrode 601 are used as the cathode and the anode, respectively, the combination concerning the carrier-transporting ability is reversed.

As a result, electrons, which cannot participate to recombination in the vicinity of the cathode side interface (the interface between the second light-emitting layer 603-2 and the third light-emitting layer 603-3) of the layer (the second light-emitting layer 603-2) containing the light-emitting substance capable of emitting light with the long wavelength, are provided with an opportunity to undergo recombination in the layer (the first light-emitting layer 603-1) which is located on the anode side and contains the light-emitting substance capable of emitting light with the short wavelength. Thus, deterioration resulting from a phenomenon that a carrier (electron or hole) reaches to a carrier-transporting layer which has carrier-transporting ability opposite to the respective carrier can be retarded, which contributes to improvement in lifetime of the light-emitting element.

Energy obtained by recombination of holes and electrons is readily transferred from a substance which emits light with a short wavelength to a substance which emits light with a long wavelength. In such a case, light emitted from the substance which emits light with the long wavelength is enhanced, which makes it difficult to balance the intensities of emissions from the substance which emits light with the short wavelength and from the substance which emits light with the long wavelength. However, by using the above-mentioned structure, the electron which fails to participate to recombination in the vicinity of the interface between the second light-emitting layer 603-2 and the third light-emitting layer 603-3 can be subjected to recombination in the layer (the first light-emitting layer 603-1) which is located on the anode side and contains the light-emitting substance capable of emitting light with the short wavelength. Thus, a well balanced emission is attainable, and an emission with desired color can be obtained.

In such a structure, when an anthracene derivative, which has electron-transporting ability as well as hole-transporting ability, is used as a host material of the first light-emitting layer 603-1 and the second light-emitting layer 603-2 in which a light-emitting substance is dispersed, the effect of improving the lifetime is more effectively obtained.

When three kinds of light-emitting substances, i.e., red, blue, and green-emissive light-emitting substances, are combined in the structure shown in FIG. 6C, it is preferred, as shown in FIG. 7B, to employ a structure in which a light-emitting layer 603 is formed as a four-layer structure containing, from the side of the first pixel electrode 600, a first light-emitting layer 603-1, a second light-emitting layer 603-2, a third light-emitting layer 603-3, and a fourth light-emitting layer 603-4 and in which the layer (the third light-emitting layer 603-3) containing a green-emissive light-emitting substance 604-7 and the layer (the second light-emitting layer 603-2) containing a red-emissive light-emitting substance 604-6 are sandwiched between the layers (the first light-emitting layer 603-1 and the fourth light-emitting layer 603-4) containing a blue-emissive light-emitting substance 604-5. Note that, in the structure shown in FIG. 7B, carrier-transporting ability of each of the light-emitting layers is tuned to allow the region for recombination of holes and electrons to be located in the vicinity of the interface between the cathode-side layer (the fourth light-emitting layer 603-4) containing the blue-emissive light-emitting substance 604-5 and the layer (the third light-emitting layer 603-3) containing the green-emissive light-emitting substance 604-7. By using such structure, the lifetime of the light-emitting element can be improved, and the emission from the light-emitting substance capable of emitting light with the long wavelength and that from the light-emitting substance capable of emitting light with the short wavelength can be readily balanced.

Note that, when the first pixel electrode 600 and the second pixel electrode 601 are respectively the anode and cathode, recombination in the vicinity of the interface between the fourth light-emitting layer 603-4 and the third light-emitting layer 603-3 can be achieved by designing the light-emitting element so that: the cathode-side layer (the fourth light-emitting layer 603-4) containing the blue-emissive light-emitting substance 604-5 has electron-transporting ability; and the layer (the third light-emitting layer 603-3) containing the green-emissive light-emitting substance 604-7, the layer (the second light-emitting layer 603-2) containing the red-emissive light-emitting substance 604-6, and the anode-side layer (the first light-emitting layer 603-1) containing the blue-emissive light-emitting substance 604-5 have hole-transporting ability. When the first pixel electrode 600 and the second pixel electrode 601 are the cathode and the anode, respectively, the carrier-transporting ability of each layer is reversed. Note that carrier-transporting ability of each of the light-emitting layers can be determined by carrier-transporting ability of the substance which is contained at the highest composition in the corresponding light-emitting layers.

As a result, electrons, which cannot participate to recombination in the vicinity of the interface between the cathode-side layer (the fourth light-emitting layer 603-4) containing the blue-emissive light-emitting substance 604-5 and the layer (the third light-emitting layer 603-3) containing the green-emissive light-emitting substance 604-7, are provided with an opportunity to undergo recombination in the anode-side layer (the first light-emitting layer 603-1) containing the blue-emissive light-emitting substance 604-5. Thus, deterioration resulting from a phenomenon that a carrier (electron or hole) reaches to a carrier-transporting layer which has carrier-transporting ability opposite to the respective carrier can be retarded, which contributes to improvement in lifetime of the light-emitting element.

Energy obtained by recombination of holes and electrons is readily transferred from a substance which emits light with a short wavelength to a substance which emits light with a long wavelength. In such a case, light emitted from the substance which emits light with the long wavelength is enhanced, which makes it difficult to balance the intensities of emissions from the substance which emits light with the short wavelength and from the substance which emits light with the long wavelength. However, by using the above-mentioned structure, the electron which once fails to participate to recombination is subjected to recombination in the anode-side layer (the first light-emitting layer 603-1) containing the blue-emissive light-emitting substance 604-5, giving an emission of light with the short wavelength. Thus, a well-balanced emission is attainable, and an emission with desired color can be obtained.

The light-emitting substance used is not particularly limited, and known fluorescent substances or phosphorescent substances can be used. As fluorescent substances, for example, in addition to N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine (abbreviation: YGA2S) and 4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine (abbreviation: YGAPA), and the like, there are fluorescent substances with an emission peak equal to or greater than 450 nm, such as 4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene (abbreviation: TBP), 4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBAPA), N,N′-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine] (abbreviation: DPABPA), N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine (abbreviation: DBC 1), coumarin 30, N-(9,10-diphenyl-2-anthryl)-N, 9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCAPA), N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCABPhA), N-(9,10-diphenyl-2-anthryl)-N,N′,N-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine (abbreviation: 2DPABPhA), 9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine (abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine (abbreviation: DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone (abbreviation: DPQd), rubrene, 5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT), 2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile (abbreviation: DCM1), 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCM2), N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation: p-mPhTD), 7,13-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine (abbreviation: p-mPhAFD), 2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTI), 2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM), and 2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: BisDCJTM). As phosphorescent substances, for example, in addition to bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), there are phosphorescent substances with an emission wavelength in the range of 470 nm to 500 nm, such as bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)picolinate (abbreviation: FIrpic), bis[2-(3′,5′bistrifluoromethylphenyl)pyridinato-N,C^(2′)]iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)), and bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIracac); phosphorescent materials with an emission wavelength equal to or greater than 500 nm (materials which emit green light), such as tris(2-phenylpyridinato)iridium(III) (abbreviation: Ir(ppy)₃), bis(2-phenylpyridinato)iridium(III)acetylacetonate (abbreviation: Ir(ppy)₂(acac)), bis(1,2-diphenyl-1H-benzimidazolato)iridium(III)acetylacetonate (abbreviation: Ir(pbi)₂(acac)), tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: Tb(acac)₃(Phen)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)₂(acac)), bis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: Ir(dpo)₂(acac)), bis[2-(4′-perfluorophenylphenyl)pyridinato]iridium(III)acetylacetonate (abbreviation: Ir(p-PF-ph)₂(acac)), bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: Ir(bt)₂(acac)), bis[2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C^(3′)]iridium(III)acetylacetonate (abbreviation: Ir(btp)₂(acac)), bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: Ir(piq)₂(acac)), (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq)₂(acac)), (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: Ir(tppr)₂(acac)), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinatoplatinum(II) (abbreviation: PtOEP), tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM)₃(Phen)), and tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA)₃(Phen)). The light-emitting substances can be selected from the above-mentioned materials or other known materials in consideration of emission colors (or peak wavelengths of an emission) of each of the light-emitting layers.

When the host material is used, the following can be given: metal complexes such as tris(8-quinolinolato)aluminum(III) (abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq₃), bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), and bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); heterocyclic compounds such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), and 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11); and aromatic amine compounds such as NPB (or α-NPD), TPD, and BSPB. In addition, condensed polycyclic aromatic compounds such as anthracene derivatives, phenanthrene derivatives, pyrene derivatives, chrysene derivatives, and dibenzo[g,p]chrysene derivatives are given. The following is specifically given as the condensed polycyclic aromatic compound: 9,10-diphenylanthracene (DPAnth); N,N-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (CzA1PA); 4-(10-phenyl-9-anthryl)triphenylamine (DPhPA); 4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine (YGAPA); N,9-diphenyl-N-[4-(l 0-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (PCAPA); N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine (PCAPBA); N-9-diphenyl-N-(9,10-diphenyl-2-anthryl)-9H-carbazol-3-amine (2PCAPA); 6,12-dimethoxy-5,11-diphenylchrysene, N,N,N′,N′,N″,N″,N″′,N″′-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetramine (DBC 1); 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (CzPA); 3,6-diphenyl-9-[4-(10-phenyl-9-antryl)phenyl]-9H-carbazole (DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene (DPPA), 9,10-di(2-naphthyl)anthracene (DNA), 2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA), 9,9′-bianthryl (BANT), 9,9′-(stilbene-3,3′-diyl)diphenanthrene (DPNS), 9,9′-(stilbene-4,4′-diyl)diphenanthrene (DPNS2), 3,3′,3″-(benzene-1,3,5-triyl)tripyrene (TPB3) and the like. From these substances or other known substances, the host material may be selected so that the host material has a larger energy gap (or a triplet energy if the light-emitting substance emits phosphorescence) than the light-emitting substance dispersed in the light-emitting layer and has carrier-transporting ability required for each of the light-emitting layers.

The electron-transporting layer is a layer that contains a substance with high electron-transporting ability. For example, a layer containing a metal complex having a quinoline skeleton or a benzoquinoline skeleton, such as tris(8-quinolinolato)aluminum (abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃), bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂), or bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation: BAlq) can be used. Alternatively, a metal complex having an oxazole-based or thiazole-based ligand, such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂) or bis[2-(2-hydroxyphenyl)-benzothiazolato]zinc (abbreviation: Zn(BTZ)₂) can be used. Besides the metal complexes, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (abbreviation: OXD-7), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), or the like can also be used. The substances described here are mainly those having electron mobility of 10⁻⁶ cm²/Vs or more. It is to be noted that a substance other than the above substances may be used as long as it has higher electron-transporting ability than hole transporting ability.

Further, the electron-transporting layer may be formed as not only a single layer but also as a stacked layer in which two or more layers formed using the above mentioned substances are stacked.

Further, a layer for controlling transport of electron may be provided between the electron-transporting layer and the light-emitting layer. Note that the layer for controlling transport of electron is a layer in which a small amount of a substance having high electron-trapping ability is added to a layer containing the above-mentioned substances having high electron-transporting ability. The layer for controlling transport of electron controls transport of electron, which enables adjustment of carrier balance. Such a structure is very effective in suppressing a problem (such as shortening of element lifetime) caused by a phenomenon that electron passes through the light-emitting layer.

Further, an electron injection layer may be provided so as to be in contact with an electrode functioning as a cathode. As the electron injection layer, alkali metal, alkaline earth metal, or a compound of thereof such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF₂), and the like can be employed. For example, a layer which contains both a substance having electron-transporting ability and an alkali metal, an alkaline earth metal, or a compound thereof (a layer of Alq including magnesium (Mg) for example) can be used. Note that electron can be efficiently injected from the cathode by using, as the electron injection layer, a substance having electron-transporting ability to which an alkali metal or an alkaline earth metal is mixed.

When the second pixel electrode 601 is used as the cathode, a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a low work function (specifically, work function of smaller than or equal to 3.8 eV), can be used as a substance for the second pixel electrode 601. As a specific example of such a cathode material, an element belonging to Group 1 or Group 2 in the periodic table, i.e., an alkali metal such as lithium (Li) or cesium (Cs), or an alkaline earth metal such as magnesium (Mg), calcium (Ca), or strontium (Sr); an alloy containing any of these metals (such as MgAg or AlLi); a rare earth metal such as europium (Eu) or ytterbium (Yb); an alloy containing such a rare earth metal; or the like can be used. However, when the electron injection layer is provided between the cathode and the electron-transporting layer, any of a variety of conductive materials such as Al, Ag, ITO, and indium oxide-tin oxide containing silicon or silicon oxide, and the like can be used regardless of its work function as the cathode. Films of these electrically conductive materials can be formed by a sputtering method, an ink-jet method, a spin coating method, or the like.

It is preferable that, when the second pixel electrode 601 is used as the anode, the second pixel electrode 601 is formed using a metal, an alloy, or a conductive compound, a mixture thereof, or the like having a high work function (specifically greater than or equal to 4.0 eV). Specifically, an example thereof is indium oxide-tin oxide (ITO: indium tin oxide), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide (IZO: indium zinc oxide), indium oxide containing tungsten oxide and zinc oxide (IWZO), or the like. Such conductive metal oxide films are usually formed by a sputtering method, but may also be formed by using a sol-gel method or the like. For example, indium zinc oxide (IZO) can be formed by a sputtering method using a target in which 1 to 20 wt % of zinc oxide is added to indium oxide. Indium oxide containing tungsten oxide and zinc oxide (IWZO) can be formed by a sputtering method using a target in which 0.5 wt % to 5 wt % of tungsten oxide and 0.1 wt % to 1 wt % of zinc oxide are contained in indium oxide. In addition, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), a nitride of a metal (such as titanium nitride), or the like can be given. By forming the above-mentioned composite material so as to be in contact with the anode, a material for the anode can be selected regardless the magnitude of its work function.

Note that, as to the above-mentioned EL layer, a plurality of EL layer may be formed between the first pixel electrode 600 and the second pixel electrode 601 as shown in FIG. 8. In this case, a charge generation layer 803 is preferably provided between the stacked EL layers 800 and 801. The charge generation layer 803 can be formed by using the above-mentioned composite material. Further, the charge generation layer 803 may have a stacked structure comprising a layer containing the composite material and a layer containing another material. In this case, as the layer containing another material, a layer containing an electron donating substance and a substance with high electron-transporting ability, a layer comprising a transparent conductive material, and the like can be used. Such a structure allows the formation of a light-emitting element with high emission efficiency and a long lifetime. Moreover, a light-emitting element which provides a phosphorescent emission from one of the EL layers and a fluorescent emission from the other of the EL layers can be readily obtained. Note that this structure can be combined with the above-mentioned structures of the EL layer. For instance, the EL layer having the structure of FIG. 6C and the EL layer having the structure of FIG. 6A can be stacked. Specifically, it is readily achieved to obtain blue and green fluorescent emissions from the EL layer 800 having the structure of FIG. 6C and simultaneously obtain a red phosphorescent emission from the EL layer 801 having the structure of FIG. 6A, where the charge generation layer 803 is sandwiched therebetween. In a similar way, green and red phosphorescent emissions are obtained from the EL layer 800 having the structure of FIG. 6C, and a blue fluorescent emission is simultaneously obtained from the EL layer 801 having the structure of FIG. 6A, where the charge generation layer 803 is sandwiched therebetween. In particular, the structure which provides the green and red phosphorescent emissions and the blue fluorescent emission is preferred since a white emission with well-balanced emission efficiencies of the EL layers is attainable.

Through the above-mentioned process, the light-emitting devices shown in FIGS. 1A to 1C can be obtained.

After the formation of the element formation layer and the light-emitting layer, it is preferred to seal the light-emitting element with an organic resin 400, a protective film 401, and the like as shown in FIGS. 4A and 4B in order to prevent a substance which promotes deterioration of the EL layer from entering from the outside. A sealing substrate may be used instead of the organic resin 400 and the protective film 401. However, the protective film 401 is not necessarily formed over input and output terminals which are connected to an FPC and the like later.

Since the light-emitting device of the present embodiment displays an image toward the plastic substrate 110 side through the color filter, it is possible to use the above-mentioned organic resin 400, the protective film 401, and the sealing substrate even if they are colored or have low transmissivity with respect to visible light. In the case where the organic resin 400, the protective film 401, and the sealing substrate each are formed using light-transmitting materials, a monochromic image can be also supplied from the sealing substrate side if the second pixel electrode is formed by a light-transmitting material or in a shape which allows visible light to be transmitted therethrough. A material similar to that for the plastic substrate 110 can be used for the sealing substrate.

Next, the FPC 402 is bonded to each of electrodes of the input and output terminals with an anisotropic conductive material. An IC chip may be mounted thereover if necessary.

By the above-mentioned process, manufacture of a module of the light-emitting device to which the FPC 402 is connected is completed.

Note that, in the case where the semiconductor layer of the TFT included in the light-emitting device of the present embodiment is not subjected to treatment performed at a high-temperature or a laser irradiation, a structure shown in FIG. 2 can be employed.

In the structure shown in FIG. 2, an adhesive 111 is provided over a plastic substrate 110 and bonds an element formation layer formed over a first insulating layer 112 to the plastic substrate 110. A color filter 300 is provided over the first insulating layer 112, and a TFT 302 is provided while a second insulating layer 301 formed over the color filter 300 is sandwiched between the color filter 300 and the TFT 302. The second insulating layer 301 can be formed by using an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, silicon nitride oxide, and the like or an organic insulating material such as an acrylic, a polyimide, and the like. The use of the organic insulating material is preferred since the organic insulating material can reduce a step caused by formation of the color filter 300. Furthermore, it is preferred to provide a protective insulating film over the second insulating layer 301 in order to suppress an adverse influence of contaminant, such as a gas released from the color filter 300, upon the TFT 302. The protective insulating film is preferably formed using an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, silicon nitride oxide, and the like. In particular, it is preferred to use silicon nitride or silicon nitride oxide which has a composition of nitrogen higher than that of oxygen. Note that the protective insulating film is not necessarily provided in the case where the second insulating layer 301 is formed by an inorganic insulating film.

As shown in FIGS. 1A to 1C, after a separation layer and the first insulating layer 112 are formed, the color filter 300 and the second insulating layer 301 are formed over a substrate with low flexibility, which is followed by the formation of the TFT 302. The TFT 302 may have a known structure and be formed by a known method which does not require high temperature treatment. For instance, a TFT having a semiconductor such as the above-mentioned microcrystalline semiconductor, the amorphous semiconductor, the oxide semiconductor, the semiconductor containing an organic material as a main component, and the like is exemplified. After forming the TFT 302, a first pixel electrode 303 of a light-emitting element and a partition layer 304 are formed. Then, the separation is carried out in a similar manner to that mentioned above to achieve the transfer to a plastic substrate 110, leading to the formation of a light-emitting device similarly to that shown in FIGS. 1A to 1C.

In the light-emitting device with such a structure, the second insulating layer 301 is singly able to suppress adverse influence of a contaminant from the color filter 300 upon the TFT 302 and the light-emitting element, which contributes to reduction of manufacturing process.

It should be noted that even in the structure shown in FIG. 2, the color filter is formed using the substrate with low flexibility. Therefore, similarly to the structure shown in FIGS. 1A to 1C, the light-emitting device with the structure of FIG. 2 can display a full color image with high resolution in spite of its flexibility.

Embodiment 2

A top view and a sectional view of a module of a light-emitting device (also referred to as an EL module) are illustrated in FIGS. 4A and 4B, respectively.

FIG. 4A is a top view showing the EL module, and FIG. 4B is a view showing a part of a cross section taken along line A-A′ of FIG. 4A. In FIG. 4A, an insulating layer 501 is formed over a plastic substrate 110 with an adhesive 500 (for example, the second adhesive and the like) sandwiched therebetween, over which a pixel portion 502, a source side driving circuit 504, and a gate side driving circuit 503 are formed. These elements can be obtained by the manufacturing method demonstrated in embodiment 1.

Reference numerals 400 and 401 denote an organic resin and a protective film, respectively, and the pixel portion 502, the source side driving circuit 504, and the gate side driving circuit 503 are covered by the organic resin 400 which is further covered by the protective film 401. Sealing by a cover material can be further conducted by using an adhesive. The cover material can be bonded as a supporting base before the separation process.

A reference numeral 508 denotes a wiring for transmitting signals inputted to the source side driver circuit 504 and the gate side driver circuit 503 and receives video signals, clock signals, and the like from an FPC (Flexible Printed Circuit) 402 which functions as an external input terminal. Although only the FPC 402 is depicted in FIGS. 4A and 4B, a printed wiring board (PWB) may be provided to the FPC 402. The light-emitting device according to the embodiments of the invention includes not only a light-emitting device itself but also a state in which an FPC or a PWB is attached thereto.

Next, a sectional structure is described with reference to FIG. 4B. The insulating layer 501 is provided over and in contact with the adhesive 500, and the pixel portion 502 and the gate side driving circuit 503 are formed over the insulating layer 501. The pixel portion 502 comprises a plurality of pixels 515, and the plurality of pixels 515 include a current control TFT 511 and a first pixel electrode 512 which is electrically connected to one of source and drain electrodes of the current control TFT 511. Although FIG. 4B shows only one of the plurality of pixels 515, they are arranged in a matrix form in the pixel portion 502. The gate side driver circuit 503 is formed using a CMOS circuit in which a plurality of n-channel TFTs 513 and a plurality of p-channel TFTs 514 are combined.

Embodiment 3

In this embodiment, electronic devices which include the light-emitting devices described in embodiments 1 and 2 are described.

Examples of the electronic devices which include the light-emitting devices described in embodiments 1 or 2 include cameras such as video cameras and digital cameras, goggle type displays, navigation systems, audio playback devices (e.g., car audio systems and audio systems), computers, game machines, portable information terminals (e.g., mobile computers, mobile phones, portable game machines, and electronic books), image playback devices in which a recording medium is provided (specifically, devices that are capable of playing back recording media such as digital versatile discs (DVDs) and equipped with a display unit that can display images), and the like. Specific examples of such electronic devices are shown in FIGS. 5A to 5D.

FIG. 5A illustrates a television device which includes a housing 9101, a supporting base 9102, a display portion 9103, speaker portions 9104, video input terminals 9105, and the like. The television device is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion 9103. The television device, in which the flexible light-emitting device capable of displaying a full color image with high resolution is mounted, allows the display portion 9103 to possess a curved shape, is lightweight, and supplies an image with high quality.

FIG. 5B illustrates a computer which includes a main body 9201, a housing 9202, a display portion 9203, a keyboard 9204, an external connection port 9205, a pointing device 9206, and the like. The computer is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion 9203. The computer, in which the flexible light-emitting device capable of displaying a full color image with high resolution is mounted, allows the display portion 9203 to possess a curved shape, is lightweight, and supplies an image with high quality.

FIG. 5C illustrates a mobile phone, which includes a main body 9401, a housing 9402, a display portion 9403, an audio input portion 9404, an audio output portion 9405, operation keys 9406, an external connection port 9407, an antenna 9408, and the like. The mobile phone is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion 9403. The mobile phone, in which the flexible light-emitting device capable of displaying a full color image with high resolution is mounted, allows the display portion 9403 to possess a curved shape, is lightweight, and supplies an image with high quality. In addition, the lightweight mobile phone can have appropriate weight even if a variety of additional values are added thereto, and thus the mobile phone is suitable as a highly functional mobile phone.

FIG. 5D illustrates a camera which includes a main body 9501, a display portion 9502, a housing 9503, an external connecting port 9504, a remote control receiving portion 9505, an image receiving portion 9506, a battery 9507, an audio input portion 9508, operation keys 9509, an eyepiece portion 9510, and the like. The camera is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion 9502. The camera, in which the flexible light-emitting device capable of displaying a full color image with high resolution is mounted, allows the display portion 9502 to possess a curved shape, is lightweight, and supplies an image with high quality.

FIG. 5E illustrates a flexible display which includes a main body 9601, a display portion 9602, an insert portion of an external memory 9603, a speaker portion 9604, operation keys 9605, and the like. A television receiving antenna, an external input, an external output terminal, a battery, and the like may be mounted on the main body 9601. The flexible display is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion 9602. The display portion 9602 can possess a curved shape, is lightweight, and supplies an image with high quality. When the display portions of the electronic devices shown in FIGS. 5A to 5D are manufactured so as to have a curved shape and the flexible display shown in FIG. 5E is mounted on the display portions, a electronic device having a display portion with a curved shape can be supplied.

As described above, the range of application of the light-emitting device manufactured by using the light-emitting element shown in embodiment 1 or 2 is extremely wide, and the light-emitting device can be applied to electronic devices in a wide variety of fields.

This application is based on Japanese Patent Application serial no. 2008-180229 filed with Japan Patent Office on Jul. 10, 2008, the entire contents of which are hereby incorporated by reference.

EXPLANATION OF REFERENCE

-   -   110: plastic substrate, 111: adhesive, 112: insulating layer,         113: element formation layer, 114: TFT, 115: TFT of driving         circuit portion, 116: color filter, 117: first pixel electrode,         118: partition layer, 119: EL layer, 120: second pixel         electrode, 121: light-emitting element, 122: first protective         insulating film, 123: second protective insulating film, 124:         color filter, 200: substrate, 201: separation layer, 202:         provisional supporting substrate, 203: first adhesive, 204:         second adhesive, 300: color filter, 301: second insulating         layer, 302: TFT, 303, first pixel electrode, 304: partition         layer, 400: organic resin, 401: protection film, 402: FPC, 500:         adhesive, 501: insulating layer, 502: pixel portion, 503: gate         side driving circuit, 504: source side driving circuit, 508:         wiring, 511: current control TFT, 512, first pixel electrode,         513: n-channel TFT, 514: p-channel TFT, 600: first pixel         electrode, 601: second pixel electrode, 602: EL layer, 603:         light-emitting layer, 603-1: first light-emitting layer, 603-2:         second light-emitting layer, 603-3: third light-emitting layer,         603-4, fourth light-emitting layer, 604: light-emitting         substance, 604-1: light-emitting substance, 604-2:         light-emitting substance, 604-5: blue-emissive light-emitting         substance, 604-6: red-emissive light-emitting substance, 604-7:         green-emissive light-emitting substance, 800: EL layer, 801: EL         layer, 803: charge generation layer, 9101: housing, 9102:         supporting base, 9103: display portion, 9104: speaker portion,         9105: video input terminal, 9201: main body, 9202: supporting         base, 9203: display portion, 9204: keyboard, 9205: external         connection port, 9206: pointing device, 9401: main body, 9402:         housing, 9403: display portion, 9404: audio input portion, 9405:         audio output portion, 9406: operation key, 9407: external         connection port, 9408: antenna, 9501: main body, 9502: display         portion, 9503: housing, 9504: external connecting port, 9505:         remote control receiving portion, 9506: image receiving portion,         9507: battery, 9508: audio input portion, 9509: operation key,         9510: eyepiece portion. 9601: main body, 9602: display portion,         9603: insert portion of external memory, 9604: speaker portion,         9605: operation key. 

What is claimed is:
 1. A light-emitting device comprising: a substrate; an oxide semiconductor over the substrate; a gate electrode over the oxide semiconductor; a first insulating film over the gate electrode, the first insulating film comprising an inorganic insulating material; a source electrode and a drain electrode electrically connected to the oxide semiconductor; and a light-emitting element electrically connected to one of the source electrode and the drain electrode, wherein the light-emitting element comprises: an anode; a first light-emitting layer over the anode; a second light-emitting layer over the first light-emitting layer; a third light-emitting layer over the second light-emitting layer; a fourth light-emitting layer over the third light-emitting layer; and a cathode over the fourth light-emitting layer, wherein the first light-emitting layer comprises a first light-emitting substance and a first host material, wherein the second light-emitting layer comprises a second light-emitting substance and a second host material, wherein the third light-emitting layer comprises a third light-emitting substance and a third host material, wherein the fourth light-emitting layer comprises a fourth light-emitting substance and a fourth host material, wherein each of the first light-emitting substance and the fourth light-emitting substance is configured to emit blue light having a shorter wavelength than a wavelength of each of the second light-emitting substance and the third light-emitting substance, wherein the first light-emitting substance is the same as the fourth light-emitting substance, wherein the second light-emitting substance is configured to emit red light, wherein the fourth light-emitting substance is different from the second light-emitting substance and the third light-emitting substance, and wherein the fourth host material is different from the second host material and the third host material.
 2. The light-emitting device according to claim 1, wherein the oxide semiconductor comprises indium, gallium, and zinc.
 3. A light-emitting device comprising: a substrate; an oxide semiconductor over the substrate; a gate electrode over the oxide semiconductor, the gate electrode overlapping with the oxide semiconductor; a first insulating film over the gate electrode, the first insulating film comprising an inorganic insulating material; a source electrode and a drain electrode electrically connected to the oxide semiconductor; a color filter over the first insulating film; a second insulating film over the color filter; and a light-emitting element over the second insulating film and electrically connected to one of the source electrode and the drain electrode, wherein the color filter comprises a region overlapping with the light-emitting element through the second insulating film, wherein the color filter and the oxide semiconductor do not overlap each other, wherein the color filter and the gate electrode do not overlap each other, wherein the first insulating film is positioned between the oxide semiconductor and the color filter, and between the gate electrode and the color filter, wherein the light-emitting element comprises: an anode; a first light-emitting layer over the anode; a second light-emitting layer over the first light-emitting layer; a third light-emitting layer over the second light-emitting layer; a fourth light-emitting layer over the third light-emitting layer; and a cathode over the fourth light-emitting layer, wherein the first light-emitting layer comprises a first light-emitting substance and a first host material, wherein the second light-emitting layer comprises a second light-emitting substance and a second host material, wherein the third light-emitting layer comprises a third light-emitting substance and a third host material, wherein the fourth light-emitting layer comprises a fourth light-emitting substance and a fourth host material, wherein each of the first light-emitting substance and the fourth light-emitting substance is configured to emit blue light having a shorter wavelength than a wavelength of each of the second light-emitting substance and the third light-emitting substance, wherein the first light-emitting substance is the same as the fourth light-emitting substance, wherein the second light-emitting substance is configured to emit red light, wherein the fourth light-emitting substance is different from the second light-emitting substance and the third light-emitting substance, and wherein the fourth host material is different from the second host material and the third host material.
 4. The light-emitting device according to claim 3, wherein the oxide semiconductor comprises indium, gallium, and zinc.
 5. A light-emitting device comprising: a substrate; a first light-emitting element, a second light-emitting element, a third light-emitting element, and a fourth light-emitting element over the substrate; a first color filter comprising a region overlapping with the first light-emitting element, the first color filter configured to transmit red light; a second color filter comprising a region overlapping with the second light-emitting element, the second color filter configured to transmit green light; and a third color filter comprising a region overlapping with the third light-emitting element, the third color filter configured to transmit blue light, wherein the fourth light-emitting element does not overlap with any color filters, wherein the first light-emitting element is electrically connected to a first transistor, wherein the second light-emitting element is electrically connected to a second transistor, wherein the third light-emitting element is electrically connected to a third transistor, wherein the fourth light-emitting element is electrically connected a fourth transistor, wherein each of the first transistor, the second transistor, the third transistor, and the fourth transistor comprises an oxide semiconductor, and a gate electrode over the oxide semiconductor, wherein the first color filter does not overlap with the first transistor, wherein the second color filter does not overlap with the second transistor, wherein the third color filter does not overlap with the third transistor, wherein each of the first light-emitting element, the second light-emitting element, the third light-emitting element, and the fourth light-emitting element comprises: an anode; a first light-emitting layer over the anode; a second light-emitting layer over the first light-emitting layer; a third light-emitting layer over the second light-emitting layer; a fourth light-emitting layer over the third light-emitting layer; and a cathode over the fourth light-emitting layer, wherein the first light-emitting layer comprises a first light-emitting substance and a first host material, wherein the second light-emitting layer comprises a second light-emitting substance and a second host material, wherein the third light-emitting layer comprises a third light-emitting substance and a third host material, wherein the fourth light-emitting layer comprises a fourth light-emitting substance and a fourth host material, wherein each of the first light-emitting substance and the fourth light-emitting substance is configured to emit blue light having a shorter wavelength than a wavelength of each of the second light-emitting substance and the third light-emitting substance, wherein the first light-emitting substance is the same as the fourth light-emitting substance, wherein the second light-emitting substance is configured to emit red light, wherein the fourth light-emitting substance is different from the second light-emitting substance and the third light-emitting substance, and wherein the fourth host material is different from the second host material and the third host material.
 6. The light-emitting device according to claim 5, wherein the oxide semiconductor comprises indium, gallium, and zinc. 